When and where the earliest modern human populations migrated and settled in East Asia are relatively well known. However, how these populations moved between islands on treacherous stretches of sea is still shrouded in mystery. In two new papers, researchers from Japan and Taiwan led by Professor Yousuke Kaifu from the University of Tokyo simulated methods ancient peoples would have needed to accomplish these journeys, and they used period-accurate tools to create the canoes to make the journey themselves.
Evidence suggests that around 30,000 years ago, humans made a sea crossing — without maps, metal tools or modern boats — from what is now called Taiwan to some of the islands in southern Japan, including Okinawa. To find out exactly how this crossing was made, a team led by Kaifu performed various simulations and experiments, including the use of physical recreations, to learn the most plausible way this crossing was achieved. Of the two newly published papers, one used numerical simulations to cross one of the strongest currents in the world called the Kuroshio. The simulation showed that a boat made using tools of the time, and the right know-how, could have navigated the Kuroshio. The other paper detailed the construction and testing of a real boat which the team successfully used to paddle between islands over 100 kilometers apart.
"We initiated this project with simple questions: 'How did Paleolithic people arrive at such remote islands as Okinawa?' 'How difficult was their journey?' 'And what tools and strategies did they use?'" said Kaifu. "Archaeological evidence such as remains and artifacts can't paint a full picture as the nature of the sea is that it washes such things away. So, we turned to the idea of experimental archaeology, in a similar vein to the Kon-Tiki expedition of 1947 by Norwegian explorer Thor Heyerdahl."
In 2019, the team constructed a 7.5-meter dugout canoe called Sugime, built from a single Japanese cedar trunk, using replicas of 30,000-year-old stone tools. They paddled it 225 kilometers from eastern Taiwan to Yonaguni Island in the Ryukyu group, which includes Okinawa, navigating only by the sun, stars, swells and their instincts. They paddled for over 45 hours across the open sea, mostly without any visibility of the island they were targeting. Several years later, the team is still unpicking some of the data they created during the experiment, and use what they find to inform or test models about various aspects of sea crossings in that region so long ago.
"A dugout canoe was our last candidate among the possible Paleolithic seagoing crafts for the region. We first hypothesized that Paleolithic people used rafts, but after a series of experiments, we learned that these rafts are too slow to cross the Kuroshio and are not durable enough," said Kaifu. "We now know that these canoes are fast and durable enough to make the crossing, but that's only half the story. Those male and female pioneers must have all been experienced paddlers with effective strategies and a strong will to explore the unknown. We do not think a return journey was possible. If you have a map and know the flow pattern of the Kuroshio, you can plan a return journey, but such things probably did not take place until much later in history."
To understand whether such a journey could have been made in different circumstances, the team also used advanced ocean models to simulate hundreds of virtual voyages. These simulations tested different starting points, seasons and paddling strategies under both modern and ancient ocean conditions.
"I major in oceanography and use numerical methods and particle tracking techniques to research things like eel and salmon migrations, pumice drift after volcanic eruptions, and oil spills in the Gulf of Mexico," said Yu-Lin Chang from the Japan Agency for Marine-Earth Science and Technology, and a visiting researcher at UTokyo and lead author of one of the papers in this study. "The Kuroshio Current is generally considered dangerous to navigate. I thought if you entered it, you could only drift aimlessly. But the results of our simulations went far beyond what I had imagined. I'm pleased this work helped illuminate how ocean voyages may have occurred 30,000 years ago."
The simulations helped fill gaps that a one-time experiment could not. They revealed that launching from northern Taiwan offered a better chance of success than from further south, and that paddling slightly southeast rather than directly at the destination was essential for compensating against the powerful current. These findings suggest a high level of strategic seafaring knowledge among early modern humans.
"Scientists try to reconstruct the processes of past human migrations, but it is often difficult to examine how challenging they really were. One important message from the whole project was that our Paleolithic ancestors were real challengers. Like us today, they had to undertake strategic challenges to advance," said Kaifu. "For example, the ancient Polynesian people had no maps, but they could travel almost the entire Pacific. There are a variety of signs on the ocean to know the right direction, such as visible land masses, heavenly bodies, swells and winds. We learned parts of such techniques ourselves along the way."
